Implantable medical devices, such as pacemakers, determine whether capture has occurred in response to a stimulation pulse in order to determine the effectiveness of the pacing therapy administered to the patient. The term “capture” generally refers to a cardiac depolarization and contraction of the heart in response to a stimulation pulse applied by the implantable medical device.
A common technique used to determine whether capture has been effectuated is to monitor the cardiac activity of a patient and to search for presence of an evoked response following a stimulation pulse. The evoked response is an electrical event that occurs in response to the application of the stimulation pulse to the heart. The cardiac activity of the patient is monitored by the medical device by tracking stimulation pulses delivered to the heart and examining, via one or more electrodes on leads deployed within the heart, electrical activity signals that occur concurrently with depolarization or contraction of the heart.
The evoked response is often difficult to detect due to a polarization artifact present on the sensing electrode employed to sense the electrical activity of the heart. This problem is especially prevalent in pacing systems that use the same lead to deliver the stimulation pulse and sense electrical activity of the heart after delivery of the stimulation pulse. Polarization of the pacing electrode is caused by accumulation of charge on an interface between the electrode and the cardiac tissue of the heart during delivery of a stimulation pulse.
The presence of the polarization artifact on the electrode can lead to errors in evoked response detection. For example, the generated polarization artifact may result in the pacemaker identifying a false evoked response, which in turn leads to missed heartbeats. Further, the polarization signal can cause the pacemaker to fail to detect an evoked response that is in fact present.